The present invention relates in general to integrated circuit technology and in particular to amplifier stages having adjustable voltage gains within an integrated circuit.
The near-continuous development of more advanced mobile communication systems and related services have led to correspondingly low-priced and compact mobile devices that have become widely deployed. Mobile communication systems receive and amplify information signals that have widely varying amplitudes. These amplitude variations are caused by a combination of factors, including the distance between the transmitting base station and the receiving mobile device, the presence of varying obstacles in the transmission path of the signals, and the like. Variable gain amplifiers are commonly used to amplify such varying amplitude signals to a desired level.
Certain types of wireless receivers, such as wide-band CDMA receivers, require a wide range of gain control due to the large variations in the amplitudes of the received information signals. Such control may be provided by a series of cascaded transistor amplifier stages. Control switches in series with emitter resistors are used to vary the voltage-gain of such stages. When the required resolution in gain control is very fine, there may be a large number of resistors and switches per stage, which tends to increase parasitic capacitance observed at the emitter of each transistor. The parasitic capacitance then becomes a limiting factor of the frequency response and gain control resolution of the receiver circuit.
It is generally desirable to provide an improved integrated circuit layout in a receiver and in an amplifier stage in particular. It also is desirable to provide an improved integrated circuit layout so that the parasitic capacitance of the output transistor of an amplifier is not a limiting factor in the performance of the amplifier stage of a receiver.
The above-discussed deficiencies of the prior art are overcome by the present invention that provides an amplifier stage having an improved adjustable voltage gain within an integrated circuit. According to an advantageous embodiment of the present invention, an amplifier stage includes a transistor, an output load, first and second resistive elements, and first and second control switches.
The transistor includes an input terminal, an output terminal and a ground terminal. The output load has a first terminal coupled to the transistor output terminal and a second terminal coupled to a positive power supply source.
The first resistive element comprises a first resistor having a first terminal and a second terminal, and a first diode having an anode coupled to the transistor ground terminal and a cathode coupled to the first terminal of the first resistor. The second resistive element comprises a second resistor having a first terminal and a second terminal, and a second diode having an anode coupled to the transistor ground terminal and a cathode coupled to the first terminal of the second resistor.
The first control switch is capable of coupling the first diode cathode to the positive power supply source, and the second control switch is capable of coupling second diode cathode to the positive power supply source, wherein a gain of the amplifier stage is controlled by selectively closing first and second control switches.
In an advantageous related embodiment, the first and second resistive elements may further respectively comprise a first ground switch and a second ground switch. The first ground switch is capable of coupling the second terminal of the first resistor to ground when closed, and the second ground switch is capable of coupling the second terminal of the second resistor to ground when closed.
The amplifier stage of the present invention improves voltage gain control allowing a greater number of control branches than that of the PRIOR ART (introduced with respect to FIG. 1 hereafter). The cooperative introduction of the forward-biased diodes and control switches enables fine resolution in gain control, while reducing parasitic capacitance that occurs when a large number of switches and resistors are connected to the ground terminal.
It is understood multiple amplifier stages in accord herewith may suitably be cascaded to obtain a large range of gain control, with each individual stage having a sufficient number of gain control branches to obtain fine gain resolution. This implementation is, for instance, well suited for association with wireless receiver circuits, such as wide-band CDMA receivers or the like.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the Detailed Description of the Invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the Detailed Description of the Invention, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: The terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprisexe2x80x9d and derivatives thereof, mean inclusion without limitation, the term xe2x80x9corxe2x80x9d is inclusive, meaning xe2x80x9cand/orxe2x80x9d; and the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, to bound to or with, have, have a property of, or the like. Those of ordinary skill should understand that in many instances (if not in most instances), such definitions apply to prior, as well as future uses of such defined words and phrases.